Elasticizing a flexible substrate, such as a sheet of cloth or plastic film, may be accomplished by attaching a tensioned elastic member to it. When the elastic member is allowed to contract, the flexible article wrinkles or shirrs to contract in dimension along with the elastic member. The article can subsequently be stretched as though it were itself elastic. This concept is used, for example, in the manufacture of disposable diapers to provide elastic waistbands for snug, leak-resistant, body fit.
There are many commercial processes for combining elastic members with substrate materials. However, reliably combining "live" or tensioned elastics, held in cross machine direction, with a continuously moving substrate web, as is required in high speed diaper-making systems, has required relatively complex methods and apparatii. For example, the substrate web may be passed through a festoon system whereby the continuously moving web is effectively indexed. That is, the substrate web is stopped for a short time along a portion of its path while the remainder of the web continues to move within a series of accumulation rolls. An elastic ribbon may then be sequentially stretched and bonded across the temporarily stationary portion of the web. Such a web handling system is necessarily large and unrealistic for the 1000 feet per minute web speeds of modem, high speed, diaper lines.
Alternatively, an elastic ribbon may be tensioned and then heat deactivated to cause it to become inelastic after it has been elongated. Because the elastic property is deactivated, the elastic can be handled without concern for contraction forces wrinkling the substrate web during bonding. Later, after the elastic has been bonded to the substrate web, a separate heat reactivation step reestablishes the elasticity of the profiled ribbon. Because of the need for heat deactivation and reactivation, elastic material choices are limited. Such processes are complicated by the fact that whenever heat is applied to polymer elastic materials, the temperature must be accurately controlled to avoid interfering with elastic properties. Also, the important properties of spring rate and percent stretch that am available for heat reactivated elastic materials are less than those available for "live" elastics which are not reactivated with heat.
Diaper elastic members are typically either polymer ribbons or laminates of multiple polymer strands combined with nonwoven sheets. Elastic members may generally be bonded to substrates in high speed continuous processes by compression bonding, thermal bonding, and adhesive bonding.
In light of the complexity of known processes for combining tensioned elastic members with moving substrate webs, and the need for generating diaper waistbands made of tensioned elastics, it is an object of the present invention to combine elastics, held in tension in the cross machine direction, with a continuously moving substrate web in a compact, high speed process.
It is a further object of the present invention to cut an unstretched elastic member from an elasticized web and stretch it in cross machine direction on the fly prior to combining the tensioned elastic to a moving substrate web.
It is yet another object of the present invention to combine a tensioned elastic member to a moving substrate web without the need for introducing external heat to the materials.